The invention relates to an electronic module with layer of adhesive, and to a process for producing it.
Layers of adhesive in electronic modules are used for a very wide range of purposes. Electronic modules are known in which materials of a similar type, such as semiconductor chips, are mechanically joined via a layer of adhesive and stacked, or metallic surfaces are provided with corresponding metallic flat conductors, or wherein individual ceramic layers are adhesively bonded to form a multilayer ceramic substrate. Moreover, electronic modules are known in which materials of different types are joined to one another by means of a layer of adhesive, for example a semiconductor chip is joined to a metallic chip island, or a semiconductor chip is joined to a ceramic substrate or a metallic flat conductor is joined to a ceramic substrate.
The thermal and electrical properties of the layer of adhesive can be varied by admixing fillers into the layer of adhesive. Some electronic modules have electrically conductive layers of adhesive, and some electronic modules have electrically insulating layers of adhesive. One drawback of conventional layers of adhesive is that, despite having particulate fillers, they have completely isotropic properties with regard to the electrical conductivity and/or the thermal conductivity. On account of the isotropic electrical conductivity in an electrically conductive layer of adhesive, not only are metallic surfaces facing one another electrically connected to one another and short-circuited, but also electrically conductive surfaces arranged next to one another are short-circuited. The same drawback arises with layers of adhesive with an isotropic thermal conductivity, in which the thermal energy cannot be deliberately dissipated in one direction, but rather is transmitted uniformly in all directions.
A further drawback of filled layers of adhesive is their minimum thickness. Whereas the adhesive base composition of a layer of adhesive can be made as thin as desired, depending on the viscosity, with filled layers of adhesive which are intended to improve either the thermal properties or the electrical properties of the adhesive base composition, a thickness of 5 micrometers or more is required in order for the filler to be incorporated in a sufficient thickness and concentration in the adhesive base composition.
A further drawback of such thick filled layers of adhesive is that a meniscus is formed in the edge region, requiring increased area depending on the wetting properties and the adhesive thickness.